Self sealing piston



July 11, 1961 c. R. DE JOHN SELF SEALING PISTON Filed Dec. 9, 1959 UniteThis invention relates to self sealing or ringless pistons for operationin high speed engines or motors, and is especially valuable as appliedto the very small pistons of miniature motors, as used, for example, intoy boats, airplanes and automobiles.

Piston rings are well known to be inadequate as sealing means forminiature pistons, i.e., pistons having a range of about /2 inch to oneinch diameter. They must therefore be of case hardened steel, and beindividually ground and lapped to fit the respective cylinders in whichthey are to operate, the lapping operation involving the reciprocationof each piston in its cylinder, using an abrasive to bring it to thebest fit possible. Such a procedure is obviously expensive as tomaterial, time and labor, compared to the corresponding items of thepresent invention.

An object of the present invention is to greatly reduce the cost ofmaking miniature pistons and at the same time produce pistons which havea better self-sealing quality not only when new but throughout theirlives. Moreover, the improved pistons have much longer life thanconventional miniature pistons, due to the construction herein shown anddescribed.

The piston of this invention, having a much longer life, need not becase hardened, and in fact need not be made of iron or steel, but may bemade of softer metal. That is due to the fact that successive wearingsurfaces of the piston are resiliently pressed against the wall of thecylinder.

Another substantial advantage is that the construction is such that thegases, during both the compression and firing strokes, exert an outwardpressure on the peripheral piston wall, thereby improving the sealingquality and the resulting engine efficiency.

The invention also eliminates the mentioned lapping operation which hasheretofore been necessary.

The improved piston also allows smaller pistons to be made, pistons asas inch in diameter, for which there is great need and which,heretofore, could not be made commercially.

The present invention also allows the improved pistons to be made fromcommon trade stock in the form of small cylindrical rods, instead of themore expensive special material heretofore used and which must behardened.

The invention contemplates a piston with a deep annular groove orcut-out in its head end, to provide outwardly or peripherally thereofwhat in effect is a single, wide, non-split, resilient ring spacedlaterally from the body of the piston, and which is integral at one endwith the piston and integral with respect to itself and which has arelatively large gas-sealing area pressing against the wall of thecylinder throughout its wearing life.

It is to be emphasized that, since the volume of airfuel mixture in theminute cylinders is extremely small, there can be practically no leakageif the motor is to develop sufiicient power to be of any use.

The invention is further distinguished by the simple procedure and toolsrequired to make the new piston, and also by the fact that the necessarytolerance is only about three one-thousandths of an inch, as against onetates I atent 2,992,052 Patented July 11, 1961 ice ten-thousandths forthe type requiring the mentioned lapping process.

The drawings illustrate the invention, and in these:

FIGURE 1 is a side elevation of a piston a cylinder, the latter shown indotted lines;

FIG. 2 is a fragmentary enlarged section of FIG. 1;

FIG. 3 is a view similar to FIG. 2, showing a modified form of piston;and

FIG. 4 is a fragmentary section, also similar to FIG. 2, but showing asplit expansion ring Within an annular groove of the piston.

Referring to the drawings for a more detailed description, and at firstto FIGS. 1 and 2, the cylindrical piston 5, within a cylinder 6, has arelatively deep annular groove 7 extending from its upper or head enddownwardly or rearwardly, to form a resilient margin 9 outside of orperipheral to the groove. This margin is expanded in its upper portionto form a non-split or continuous ring of uniform diameter andsubstantial width, which presses against the cylinder wall, and isyieldable due to its resiliency, thereby forming a self-sealing piston.

In FIG. 3 I show a modification, which is similar to the pistondescribed above, but differs therefrom in that the peripheral margin 9Ais thicker than margin 9, and is intended for pistons of greater thanone inch in diameter, and differs also in that it has a series ofparallel annular grooves 12 which are provided to give greaterbendability to the thicker margin.

In FIG. 4, I show *a structure similar to that of FIG. 2, but, in theformer, there is an expansion split ring 15 in the annular groove, torthe purpose of providing extra pressure of the peripheral margin againstthe cylinder wall. This ring is approximately as wide or deep as thatpart of the mentioned margin which is otherwise in contact with thecylinder wall. The removal of the --'r1ng is thereby facilitated byproviding space for a tool to be inserted in the annular groove andunder the ring.

As an example of suitable piston dimensions for a A; H.P. motor, thepiston of FIG. 2 may be -7 diameter in its unexpanded portion, with alength of /2", the groove depth being A, the thickness of the peripheralwall .003", and the expansion of the latter .002" beyond the abovestated diameter.

What is claimed is:

1. A self-sealing cylindrical piston having a relatively deep annulargroove formed in its head end and of sufficient depth and adjacency tothe outer surface of the piston to render resilient the margin of thepiston peripheral to the groove, said margin expanded beyond the outsidediameter of the remaining part of the piston and of suflicient annularwidth to present a substantial area of uniform diameter for pressingcontact with the interior surface of a cylinder.

2. The piston specified in claim 1, in which said margin is relativelythick and has parallel annular grooves formed in its outer surface toprovide an adequate degree of bendability.

References Cited in the file of this patent UNITED STATES PATENTS1,020,836 Moore Mar. 19, 1912 1,224,999 Barthel May 8, 1917 2,869,524Spier Jan. 20, 1959 FOREIGN PATENTS 119,385 Germany May 27, 1900 701,093France Jim. 5. 1931

